The present invention relates to a process for preparing a shaped article from a finely particulate, granular or fibrous material as aggregate and an aqueous binder preparation which contains an acrylate polymer, wherein the aggregate is moistened with the binder preparation, made into the desired shape and then dried with or without heating.
Processes of this kind are known in a number of versions, for example from U.S. Pat. Nos 4,189,345 and 4,187,142 and from German Laid-Open application DOS 2,924,085.
The documents mentioned describe a general process wherein the aggregates are drained on a wire together with the binder, which may be a precipitate, in a sheet formation step and then dried at elevated temperature.
In this way it is possible to use for example kaolin, mineral fibers and starches to produce ceiling panels. The serious disadvantage of such basically very stiff panels is that they lose their shape in a moist room, in particular in moist and warm rooms, i.e. under tropical conditions, and sag under their own weight. Such sagging ceilings have an unattractive appearance and therefore are undesirable. A further disadvantage of such sheetlike structures is their sensitivity to microbial degredation of the starch binder, which is apparent from dark spots and the loss of mechanical strength. It is of course possible to make these panels microbicidal, for example by incorporation of formaldehyde depot materials. They ensure a gradual release of formaldehyde and give some protection against infestation. However, for protection to last any length of time it is necessary for the levels of preservative to be comparatively high, which can lead to odor nuisance and in certain circumstances to allergic reactions on the part of the inhabitants.
Other, repeatedly proven production techniques consist in moistening more or less well-ordered, usually fibrous aggregates by spraying or dipping with subsequent squeezing off and finally drying at elevated temperature under more or less compressive force to adjust the density of the sheetlike structure.
It is finally necessary to mention the generally known process for the production of chipboard, wherein the chips are sprayed with aqueous solutions usually of urea-formaldehyde condensates, and cured under pressure and temperature.
Granular aggregates are moistened with the binder preparation, the mixtures are introduced into molds, and the water is removed, usually after demolding.
As indicated, the preferred binder preparations of the prior art are almost exclusively aqueous solutions of condensation products based on phenol, melamine and/or urea with formaldehyde. Although these binders have been in use for decades, it is comparatively recently that their serious disadvantages came to light. For instance, they always contain minor amounts of starting materials, e.g. phenol and/or formaldehyde, which in the course of processing are partially emitted into the air at the workplace. This fact increasingly necessitates better ventilation of production sites. Unfortunately, in this way the compounds also pass into the atmosphere, which in turn necessitates further measures. In addition, starting materials are still present in ready-produced shaped articles and thus may end up in trace amounts in the air in the home and in the office and even in the car. Finally, these impurities cause problems with the disposal of waste as landfill if the shaped articles contain phenolic resins.